Engineering thermoplastics are a group of polymers that possess a balance of properties comprising strength, stiffness, impact resistance, and long term dimensional stability that make them useful as structural materials. Engineering thermoplastics are especially attractive in replacing metals as a viable means of reducing weight in automotive and aircraft applications, thereby increasing the fuel efficiency and payload.
Despite the attractive mechanical properties offered by engineering thermoplastics, many thermoplastics are unacceptable as structural resins where resistance to solvents is an absolute requirement. Materials such as polysulfones, undergo solvent induced cracking and crazing, especially under stress, with the loss of mechanical integrity. In addition, thermoplastics typically undergo creep under load at elevated temperatures which precludes their use in applications where high temperature dimensional stability is necessary.
Prior work has been performed in an attempt to overcome the disadvantages of engineering thermoplastics while maintaining the attractive features. For example, crystallinity has been employed to gain solvent resistance with a commercial polyetheretherketone (PEEK) as reported in Polymer, 22, 1096 (1981) and Sci,. Adv. Mater. Proc. Eng. Ser., 747 (1982). J. Polym. Sci. Polym. Chem. Ed., 20, 3131 (1982) reports the successful end capping of polysulfones with ethynyl groups, followed by crosslinking, to improve solvent resistance and U.S. Pat. No. 3,595,900 discloses a method to prepare cyanato-terminated polyarylene ethers which can be thermally crosslinked to give improved flexibility and resistance to thermal degradation.
Instead of placing reactive groups on the ends of molecules, an alternate approach to improve properties has been to incorporate reactive pendant groups along the polymer backbone. This approach gives a more effective means of crosslinking thermoplastics to improve solvent resistance while retaining good toughness and thermoformability. An example of this approach was the incorporation of pendant ethynyl groups in sulfone/ester polymers as reported in the J. Polym. Sci. Polym. Chem. Ed. 23, 2233-46, (1985) and U.S. Pat. No. 4,587,312. Pendant ethynyl and phenylethynyl groups have also been incorporated in other thermoplastics, such as polyamides and polyurethanes as reported in J. Polym. Sci. Polym. Chem. Ed. 18, 495 (1980) and Polym. Prepr. 22(1), 25-6 (1981).
The present investigation has shown a process to incorporate pendant arylcyclobutene groups in a polyaryl engineering thermoplastic to give new polymeric structures with improved properties and advantages in curing. U.S. Pat. No. 4,540,763 discloses polymeric compositions prepared by exposing poly(arylcyclobutenes) to temperatures at which the poly(arylcyclobutenes) undergo polymerization. However, the patent does not disclose the process of the present invention for preparing polyarylcyclobutenes nor the novel compositions of that process.
The present investigation has shown that pendant arylcyclobutene groups may be incorporated in a polyaryl engineering thermoplastic to give new polymeric structures with improved properties and advantages in curing.